- Erythema multiforme (EM) is a hypersensitivity reaction caused by many provoking agents including herpes simplex virus (HSV) infection (HAEM). HSV DNA sequences were identified in HAEM lesions, but infectious virus was not isolated. T cell responses were also implicated in HAEM pathogenesis, but their HSV specificity and function are still unclear. The applicants showed that viral DNA clearance is impaired in HAEM relative to HSV lesions, but clinical HAEM symptoms correlate with HSV gene expression. The HSV DNA polymerase gene (Pol) is expressed in HAEM lesions, and they are positive for CD4+ V-beta-2 T cells and IFN-gamma. Healed lesional skin were all negative. The investigator hypothesizes that HAEM is an immunopathological disease resulting from the combination of T cell responses to HSV antigens (likely Pol) and virus-mediated pathological effects. The specific aims are: (I) To examine the role of virus (Pol)-specific T cell responses in HAEM pathogenesis by establishing T cell lines/clones from HAEM lesional and healed skin and determining their HSV protein specificity and properties (viz. IFN-gamma production). ELISA spot assay will be used to estimate the clonal size of responding T cells in the skin. Both T cell clones and PBMC from HAEM and HSV patients will be examined for the presence of the skin homing receptor CLA. The second aim (II) is to examine the role of Pol in epidermal damage by determining(a) expression of the Pol accessory protein UL42 and Pol catalytic activity in HAEM lesions, and (b) the induction/activation of TGF-beta and p21waf in keratinocytes transfected with Pol or Pol/UL42 as it relates to growth arrest/apoptosis. Aim (III) is to define the route of HSV DNA transport to the skin. This will be done by determining the presence of HSV DNA fragments in CLA+ (and CD34+/CLA+) Langerhans cells (LC) precursors from HAEM and HSV patients and examining the ability of these cells to fragment HSV DNA/retain Pol DNA as they mature into LC in vitro. These studies will provide a better understanding of HAEM pathogenesis and its relationship to HSV, thereby allowing the development of novel therapies based on the targeting of disease-related HSV gene(s). They will also generate clinically relevant information for the diagnosis and management of HAEM patients as differentiated from those with EM caused by other pathogens or by drug sensitivity.